Measurement report: Sources, sinks and lifetime of NOX in a sub-urban temperate forest at night
Abstract. Through observations of NO, NO2, NOY and O3 in the Rambouillet forest near Paris, France, (as part of the ACROSS campaign, 2022) we have gained insight into nighttime processes controlling NOX in an anthropogenically impacted forest environment. O3 mixing ratios displayed a strong diel profile at the site, which was driven by a variable but generally rapid deposition to soil and foliar surfaces. The O3 diel profile was strongly influenced by relative humidity, which impacted the surface resistance to uptake, and temperature inversion, which influenced the rate of entrainment of O3 from above the canopy. Only when the O3 mixing ratio was sufficiently low (and thus the NO lifetime sufficiently long), were sustained NO peaks observed above the instrumental detection limit, enabling derivation of average NO emission rates from the soil of ~1.4 ppbv h‑1. Observations of the lack of increase in NO2 at night, despite a significant production rate from the reaction of NO with O3, enabled an effective lifetime of NO2 of ⁓0.5–3 h to be derived. As the loss of NO2 was not compensated by the formation of gas- or particle-phase reactive nitrogen species it was presumably driven by deposition to soil and foliar surfaces, or any products formed were themselves short-lived with respect to deposition. By comparison, the daytime lifetime of NO2 with respect to loss by reaction with OH is about 1 day. We conclude that the nighttime deposition of NO2 is a major sink of boundary layer NOX in this temperate forest environment.
Data used in this paper https://across.aeris-data.fr/catalogue/
Viewed (geographical distribution)